<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta http-equiv="X-UA-Compatible" content="IE=edge">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Document</title>
</head>
<body>
    <input type="button" value="弹出消息框" onclick="alert('hello world!')"/>
    <input type="button" value="添加消息" onclick="alert(document.write('<h1>hello world!<h1>'))"/>
</body>
</html>